By 2001 those satellites (flying in polar orbits and geosynchronous orbits) were equipped not only with cameras but with a range of sensors that employed the latest infrared technology.

Depending on your stretch of that definition, a satellite in a perfect polar orbit would pass over each pole once per day and might be called ‘geosynchronous’, but like the time of day at the poles the terminology becomes ambiguous.

When declared operational in 1964, Transit consisted of five satellites in offset polar orbits circling the Earth at an altitude of about 670 miles.